Part:BBa_K2711000

Glucanase

β-Glucan is a water-soluble polysaccharide that consists of glucose units. In yeast cell walls, glucose monomers are linked in a branched structure via β-(1→3) and β-(1→6) glycosidic bonds [1]. β-1,3-Glucanases (EC 3.2.1.39 and EC 3.2.1.6) catalyze the hydrolysis of glucans containing β-1,3-linked glucose monomers, one of the most abundant polysaccharides present in the yeast cell wall [2]. Bacterial endo-1,3-β-glucanases catalyze the hydrolysis of (13)-beta-D-glucosidic linkages in (1 → 3)-beta-D-glucans. These enzymes have a β-sandwich architecture and belong to the glycoside hydrolase family 16 (GH16) [3].

The UiOslo_Norway 2018 team used the sequence of endo-1,3-β-glucanase from Cellulosimicrobium cellulans (= Arthrobacter Luteus) to enable targeted lysis of yeast cells. This glucanase is also used in the commercially available product Zymolyase, among other components, which is a lytic enzyme for the digestion of yeast cell wall glucan. In our case we wanted to specifically lyse Candida albicans cells in a vaginal sample which will also contain for example bacteria and skin cells. The glucanase was synthesized by IDT after the sequence was codon optimized.

Endo-1,3-β-Glucanase

The enzyme glucanase is an important part of our detection system, as it breaks down the glucans in the yeast cell wall, making it easier to lyse the cell and access the DNA. We were not only able to successfully clone the endo-1,3-β-gluanase into the submission vector (Figure 1) and expression vector (Figure 2), but we were also able it induce its expression (Figure 3). Finally, we could also show the glucanase activity in vitro (Figure 4, Figure 5).

Figure 1: Colony PCR of glucanase in submission vector pSB1C3
Positive colonies after Two-part Gibson transformation of glucanase g-block (1-15). Glucanase at the size of 1.388 bp (blue line), colony 11 was further used after checking for correct sequence. Ladder Quick-Load 1 kb (N0468S).

Figure 2: Colony PCR of glucanase in expression vector pBAD
Positive colonies after Two-part Gibson transformation of glucanase (1-9). Glucanase at the size of 1.388 bp plus overhangs (blue line). Ladder Quick-Load 1 kb (N0468S).

The glucanase-pBAD construct was further used for protein expression. Protein expression was induced by adding arabinose (protocols).

Induction of protein expression

The induction of protein expression was verified after small-/or medium-scale cell culturing (protocol),followined by separation of proteins on a 12 % SDS-PAGE (Figure 3). The results show that the endo-1,3-β -glucanase expression was induced after addition of 0.1 % arabinose followed by a 3 h incubation at 30^oC (protocol).

Figure 3: SDS-PAGE 12 %
Uninduced (1) and induced samples (2&3) loaded on SDS-PAGE. Glucanase at the size of 52 kDa (red arrow).

Screening for Polysaccharide Endo-Hydrolases using Insoluble Dyed Polysaccharide

Insoluble dyed substrate is used to detect enzyme activity (protocol).

Figure 4: 96-well plate assay to test enzyme activity (Megazyme)
Absorbance of the glucanase was measured against diluted samples of a standard for enzyme activity (Zymolyase, Nordic Biosite). The glucanase activity was tested with samples from induced cell cultures (crude extract, supernatant and cell pellet). Absorbance was measured 1 h after loading the samples on the 96-well plate.

From Figure 4, it can be seen that the glucanase had an activity in between a 100x and 1.000x dilution of Zymolyase. Of the different cell samples from the induced cell culture, the glucanase from the supernatant had the highest enzymatic activity. We expect the glucanase to have a higher enzymatic activity after further experiments purifying the protein.

Figure 5: Plate assay to display enzyme activity (Glycospot)
Three replicates of assay. Upper left corner ‘crude cell culture’, middle left ‘supernatant’, lower left ‘positive control’ (commercially available enzyme mix), upper right ‘crude diluted’, middle right ‘pellet’, lower right ‘negative control’ (empty pBAD vector). All samples on the left parts of the plates show enzyme activity in all replicates.

Conclusion

With our results we showed that our BioBrick, the endo- 1,3-β-glucanase, has enzymatic activity and is able to cleave 1,3-β-glucan bonds. The activity is comparable to a 100x-1000x dilution of Zymolyase. Combined with either mechanical force or a detergent, we expect to be able to selectively lyse yeast cell walls.

SOURCES:

1. Deepak Mudgil, in Dietary Fiber for the Prevention of Cardiovascular Disease, 2017

2. Salazar et al., 2001. Overproduction, Purification, and Characterization of β-1,3- Glucanase Type II in Escherichia coli. Protein Expression and Purification 23, 219–225.

3. Oda et al., 2017. Structural and thermodynamic characterization of endo-1,3-β-glucanase: Insights into the substrate recognition mechanism. BBA - Proteins and Proteomics 1866 (2018) 415–425.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 958
  
• 1000
  COMPATIBLE WITH RFC[1000]